The present invention relates generally to an etching substrate material and etching process used to form high-definition patterns by etching metal materials for lead frames, shadow masks, and so on. More specifically, the invention provides a process of forming a high-definition metal pattern by surface-treating a metal substrate material by rolling, chemical polishing, physical polishing or electrolytic polishing to create a very smooth surface state, and then carrying out given etching, and a metal article processed with high definition.
For a lead frame, shadow mask or aperture grill, a photosensitive resin is first coated on the surface of a metal material. Then, the photosensitive resin is exposed to light while a desired pattern is brought in vacuum close contact therewith, thereby forming a photoresist pattern. Finally, etching is performed to form apertures, holes, etc. as desired.
For metal materials for shadow masks, alloys such as iron-nickel base alloys, and iron-nickel-cobalt base alloys are generally used. Thin alloy sheets are produced by preparing an alloy ingot by a continuous casting process or an ingot-making process, and then blooming, hot-rolling or cold-rolling the ingot.
In a conventional etching process, an exposure pattern cannot be in vacuum close contact with a substrate material having too smooth a surface at an exposure step because it is very difficult to remove gases from a central area thereof by drawing a vacuum.
Thus, the surface roughness of the metal sheet used so far in the art is Ra=ca. 0.20 to 0.70 xcexcm (center line-average surface roughness) and Rmax=ca. 2.0 to 4.0 xcexcm (maximum surface roughness).
For a shadow mask used on a computer display for high-definition display purposes, on the other hand, it is required that apertures for transmission of electron beams be located at narrow intervals and have high precision. With this, a metal should be micro-etched with an ever higher precision.
In pattern formation, the larger the amount of etching, the more slender the influence of asperities formed on the pattern becomes. However, the smaller the amount of etching, the greater the influence of the deformation of the pattern on etching becomes.
Thus, a shadow mask used on a display with high definition is obtained by micro-processing at minute intervals. In this case, however, the amount of etching is too reduced to prevent a pattern formed on the substrate from manifesting itself remarkably due to the deformation of a resist pattern. There is a strong demand for an etching substrate material and process that enable patterns to be formed with an ever higher definition.
One object of the invention is to provide an etching substrate material which enables a precisely shaped resist pattern to be formed thereon by etching. Another object of the invention is to provide a method of processing metals with high definition and producing a metal article processed with high definition. Yet another object of the invention is to provide a method of producing a high-definition processed metal article, e.g., a shadow mask, an aperture grill, and a lead frame.